Eight people who took part in the challenge have been treated at the burn center of Chicago's Loyola University Medical Center since the deep freeze happened last week, spokeswoman Chris Vicik said.

They had injuries to their "feet, arms, hands, face, and varying degrees of burns, as well," she said.

One person sought treatment at the University of Iowa Burn Treatment Center in Iowa City, spokesman Tom Moore said, and Hennepin Healthcare in Minneapolis said a "couple" of people were treated there in recent weeks.

It's not just the people throwing the water who are getting hurt. Vicik said some of the burn victims in Chicago have been those watching the stunt.

That's also what they're finding at Hennepin Healthcare, said Angie Whitley, the clinical care supervisor in the hospital's burn center.

"Some of them being parents or adults (who) go outside with their kids to do it, and the kids kind of get excited and step in the way, and the parents end up throwing the water on the children," Whitley said.

"Or, people throw it in the air just as a gust of wind comes, and (the water) catches the wind and it blows it back on them -- so we see some face scald injuries from that," she added.

Having any bare skin in weather that cold is its own problem, because it poses a risk of frostbite
.

"When it's 20 below, it's a bad idea to have uncovered skin," said Dr. Jeff Schaider, chairman of emergency medicine at Cook County Health in Chicago.

Even worse is getting water on that bare skin, he said, because it will accelerate the freezing of the skin, and increase the risk of a cold injury to the skin.

"The gamut runs from essentially being burned from hot liquid to being exposed to the cold air," he said. "If your hand has water on it, that freezes pretty quick. That's a bigger risk, actually."

Treatment depends on how severe the burn, he said. While the most common are first- and second-degree burns to the hand, Schaider said, resulting in pain and blisters, the worst cases could involve skin grafts.

Bottom line: If you want to be wowed by the science and spectacle of the boiling water challenge, watch a video. But don't try it yourself.